KR20000071876A - Liquid crystal display and light guide plate and method for manufacturing light guide plate - Google Patents

Abstract

A light guide plate capable of improving the brightness of a back light or a front light without raising the brightness of a light source, and a liquid crystal display device using the same.

On the surface opposite to the light exit surface to the liquid crystal cell in the light guide plate, a plurality of dot small recesses for reflecting the incident light from the light source in the light exit surface direction are formed, and the cross-sectional shape of the dot small recesses is triangular. At the same time, the cross-sectional inclination angle is set to 50 to 60 degrees, and the dot-shaped small concave portion makes the plane shape viewed from the direction perpendicular to the light guide plate surface almost rectangular or almost square, and at the same time the long side or almost square one side of the substantially rectangular shape. It was installed almost parallel to the longitudinal direction of this light source.

Description

Liquid crystal display, light guide plate, and manufacturing method of light guide plate {LIQUID CRYSTAL DISPLAY AND LIGHT GUIDE PLATE AND METHOD FOR MANUFACTURING LIGHT GUIDE PLATE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, a light guide plate, and a manufacturing method of a light guide plate, and more particularly, to a technology for a light guide plate in a backlight (back light) type or front light (front light) type liquid crystal display device.

In recent years, miniaturization of personal computers (P.C) has been promoted, and portable models called lap tops have become widespread. In this wrap-top type P.C, a liquid crystal display device is usually used as the display device, and the color display has been advanced these days. In such a liquid crystal display device, the liquid crystal display device called the backlight type which provided the lighting means behind the liquid crystal display panel and illuminates the whole display surface from the back occupies the mainstream. As the backlight means of such a backlight type liquid crystal display device, it is preferable that the luminance is high and there is no luminance unevenness, and the entire flat surface of the liquid crystal display panel is uniformly illuminated. In order to improve the brightness of the backlight, it is conceivable to raise the brightness of the light source. However, this increases the power consumption and the temperature rise in the liquid crystal display device.

As a backlight type liquid crystal display device, various structures are known, for example, the technique disclosed in Japanese Patent Laid-Open Nos. 4-162002, 6-67004 and the like can be cited as a conventional technique.

FIG. 2 is a diagram showing the configuration of a backlight means of a conventional backlight type liquid crystal display device, in which 1 is a light source, 2 is a light guide plate, 3 is a diffusion sheet, and 5 is a first prism The sheet, 5 'is a second prism sheet, 6 is a light scattering layer, and 7 is a reflecting sheet.

In the structure shown in FIG. 2, the light source 1 which consists of lamps, such as a cold cathode tube and a hot cathode tube, is provided in the cross section of the light guide plate 2 which consists of a light transmissive material, and the illumination light emitted from the light source 1, The light guide plate 2 is introduced into the interior. The upper surface (light emitting surface) of the light guide plate 2 is provided with a diffusion sheet 3 made of a warm white synthetic resin having a light scattering effect for uniformizing the luminance of the illumination surface over the entire surface. have. In addition, a first prism sheet 5 and a second prism sheet 5 'are provided on the upper surface for converging diffused light to some extent to improve the brightness of the front side of the liquid crystal display device.

In addition, a light scattering layer 6 for scattering light guided into the light guide plate 2 in the direction of the diffusion sheet 3 is provided on the surface (rear surface) opposite to the light exit surface of the light guide plate 2. The reflective sheet 7 is provided on the lower surface of the scattering layer 6.

The light scattering layer 6 is configured as follows. FIG. 3 is a diagram illustrating a configuration of the light scattering layer 6 in FIG. 2. As shown in FIG. 3, the light scattering layer 6 has a plurality of light scattering materials using titanium oxide, glass beads, or the like on the back surface of the light guide plate 2 in a predetermined pattern using a technique such as screen printing. It is formed by printing. Here, the light intensity from the light source 1 decreases as it moves away from the light source 1, so that the pattern area of the light diffusion layer 6 in the light guide plate 2 increases so as to move away from the light source 1. Formed.

In addition, as a substitute for the light scattering layer 6 described above, a grating groove is formed on a surface (rear surface) opposite to the light exit surface of the light guide plate, and the grating groove is configured to reflect light incident on the light guide plate. The light guide plate of is also proposed by Unexamined-Japanese-Patent No. 7-294745.

On the other hand, as a means of realizing a low power drive liquid crystal display device without using a backlight, the reflection type liquid crystal display device described in "Application material: Vol. 67, No. 10, p1159 (1998)" is known. This reflection type liquid crystal display device receives back light or sunlight and reflects incident light to a layer having a reflection function formed on the liquid crystal back surface, thereby achieving backlightlessness. However, visibility is reduced in dark places. In order to apply to a wider use environment, it is necessary to plan the countermeasure while maintaining the characteristic as a reflection type to the maximum.

As a solution to this, the front-lit liquid crystal display shown in Fig. 4 has been proposed. Fig. 4 is a diagram showing the configuration of a reflective liquid crystal display device (hereinafter referred to simply as a front light liquid crystal display device) having front light means.

In Fig. 4, 2 is a light guide plate, 6 is a light diffusion layer formed on a surface opposite to the light exit surface of the light guide plate 2 (in this case, an upper surface) (light scattering layer formed by screen printing in the same manner as the light scattering layer of Fig. 3), 1 is a light source provided in the cross section of the light guide plate 2, and the front light means is comprised by the light guide plate 2 with this light source 1 and the light scattering layer 6 attached. In the front-lit liquid crystal display shown in Fig. 4, the light source 1 is non-illuminated at a bright place, and the display is viewed by the light guide plate 2 having high transparency. When it is dark, the light source 1 is turned on so that the front light means replaces the external light.

As performance of the light guide plate of such a front-lit liquid crystal display device, it is required that scattering is small, transparency is high, and the amount of light emitted to the upper surface in FIG. 4 is small. Moreover, in the light guide plate of the front-lit liquid crystal display device, the structure which provided the grating groove in the surface on the opposite side to the light emission surface of the light guide plate 2 instead of the light scattering layer 6 of FIG. 4 is also known.

4, 31 is an absorbing film, 32 is a reflective polarizer, 33 is a diffusing film, 34 is a glass substrate, 35 is a TFT, 36 is a liquid crystal cell, 37 is a pixel electrode, 38 is a color filter, 39 is a glass substrate. , 40 is a diffusion film, 41 is a retardation film, 42 is a polarizer, and the front light type liquid crystal display device (reflective liquid crystal display device having a front light means) having such a configuration is well known, and thus detailed description of each part is omitted. do.

By the way, in the conventional backlight type liquid crystal display device shown in FIG. 2, FIG. 3, the light radiate | emitted from the light source 1 is guide | induced in the light guide plate 2, and the light-diffusion layer 6 is light-diffused. Although the structure is scattered by the material, the non-negligible portion of the amount of light incident on the light guide plate 2 is reflected by the reflective sheet 7, resulting in energy loss and the negligible amount of light incident on the light guide plate 2. Since there exists a part which radiate | emitted in the horizontal direction with respect to a liquid crystal display panel, and does not contribute to a display, the brightness improvement of a liquid crystal display device had a limit. In other words, there is a certain limitation in efficiently utilizing the light introduced into the light guide plate 2 for display.

In addition, since the light scattering layer 6 is formed by printing a light scattering material on the light guide plate 2, after the light guide plate is emitted and formed, the surface treatment is performed by plasma treatment (surface treatment for improving ink printability). The process of screen printing, ultraviolet curing, etc. was required, and manufacture of the light-guide plate 2 was also relatively inexpensive.

On the other hand, in the conventional backlight type liquid crystal display device using the light guide plate on which the grating groove is formed, the brightness is improved, but the light emitted from the light guide plate by the grating groove and the member constituting the liquid crystal display element, such as a liquid crystal cell. There is a problem that moiré occurs due to interference of regular patterns. In order to solve this problem, there is a drawback that a sheet for diffusing light strongly must be used, and as a result, sufficient luminance improvement cannot be achieved. In addition, since the grating grooves parallel to the longitudinal direction of the light source are formed to have the same cross-sectional formation to cross the light guide plate, in the case of the light guide plate having the grating grooves, it is difficult to obtain uniform luminance over the entire surface of the light guide plate. Do. It is possible to adjust the number and depth of grating grooves in the direction orthogonal to the longitudinal direction of the light source, but it is difficult to adjust the luminance in the direction parallel to the longitudinal direction of the light source, and therefore, the longitudinal direction of the light source in the light guide plate. There is a problem that the end portion in the direction parallel to the lower the luminance than the central portion, and it is difficult to equalize the luminance of the entire panel. In addition, in the case of the light guide plate in which the grating groove is formed, there is a non-uniformity of in-plane light transmittance in the liquid crystal cell itself, and even though it is required to correct this on the light guide plate side, the brightness distribution of the backlight is intentionally uneven in the light guide plate in which the grating groove is formed. The nonuniformity of the in-plane porosity of the liquid crystal cell could not be corrected.

In addition, the light guide plate on which the grating groove is formed is manufactured by injection molding, and the production of the mold for forming the light guide plate or the master stamper for forming the molding stamper is performed by forming the grating grooves one by one by a mechanical cutting operation. Therefore, it takes a lot of time and effort to manufacture a mold or a master stamper, and as a result, it is a factor that hinders the cost reduction of the light guide plate.

Moreover, in the front-lit liquid crystal display device, as a characteristic required for the light guide plate for the front light,

(1) Haze (blur) of light guide plate is small.

(2) The surface reflectance is small.

(3) Light emitted to the upper surface in FIG. 4 is small.

(4) In FIG. 4, the vertical component is large with respect to the emission direction of the emitted light.

Although the light guide plate which has the light scattering layer which printed the light scattering material, or the light guide plate in which the grating groove | channel was formed, it was difficult to obtain the light guide plate which satisfy | fills the said characteristic simultaneously. In addition, a front light type liquid crystal display device using a light guide plate having a light scattering layer printed with a light scattering material or a light guide plate having a grating groove has the same problems as those of the aforementioned backlight type liquid crystal display device. there was.

Accordingly, the technical problem to be solved by the present invention is to solve the problems of the prior art described above, and the object of the present invention is to increase the luminance of a back light or a front light without raising the luminance of a light source. It is providing the light guide plate which can aim at improvement, and the liquid crystal display device using the same.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the structure of the backlight means used for the backlight type liquid crystal display device which concerns on one Embodiment of this invention.

2 is an explanatory diagram showing a configuration of a backlight means used in a conventional backlight liquid crystal display device;

FIG. 3 is an explanatory view showing a light scattering layer made of a light scattering material formed by printing on the back surface of the light guide plate in FIG. 2; FIG.

4 is an explanatory diagram of a reflective color liquid crystal display device (conventional front light liquid crystal display device) having conventional front light means;

Fig. 5 is an explanatory diagram showing a relationship between a dot-shaped small concave portion having a triangular cross section of 55 ° in a light guide plate according to an embodiment of the present invention, and a traveling trajectory of a light source.

Fig. 6 is an explanatory diagram showing the relationship between the dot-shaped recesses having a triangular cross section of 25 ° and the traveling trajectory of the light source for contrast with the dot-shaped recesses in the embodiment of the present invention.

7A to 7C show the relationship between the printing dot, the cross-sectional ladder dot small concave portion, the dot small convex portion, and the traveling trajectory of the light source, respectively, in order to contrast with the dot small erector sphere of the embodiment of the present invention. Illustrative diagram.

FIG. 8 is an explanatory diagram showing a configuration of a front-lit liquid crystal display device (reflective color liquid crystal display device having a front light means) according to another embodiment of the present invention; FIG.

9A to 9D are explanatory diagrams showing a shape example of a dot-shaped small concave portion in the light guide plate of the embodiment of the present invention.

Fig. 10 is a table showing a preferred specific example of the dot-shaped small recess in the light guide plate of the embodiment of the present invention.

11A to 11B are explanatory diagrams showing definitions of respective numerical values and angles of dot-shaped small recesses in the light guide plate of the embodiment of the present invention.

12A to 12K are explanatory diagrams showing a manufacturing process of a light guide plate according to the embodiment of the present invention.

13 is an explanatory diagram showing a Si anisotropic etching rate.

It is a table | surface which shows the processing conditions of the Si substrate in the manufacturing process of the light guide plate which concerns on this invention.

15 is an explanatory diagram showing a configuration example of a backlight type liquid crystal display device according to the present invention;

<Explanation of symbols for the main parts of the drawings>

1: light source

2: light guide plate

3: diffusion sheet

5: first prism sheet

5 ': second prism sheet

6: light scattering layer

7: reflective sheet

31: absorbent film

32: reflective polarizer

33: diffusion film

34: glass substrate

35: TFT

36 liquid crystal cell

37: pixel electrode

38: color filter

39: glass substrate

40: diffusion film

41: retardation film

42: polarizer

In order to achieve the above object, a liquid crystal display device according to the present invention is a plurality of, for efficiently angularly changing the light introduced into the light guide plate from the light source provided on one end surface of the light guide plate in the direction of the light exit surface from the light guide plate to the liquid crystal cell. The light guide plate of the structure which provided the dot small recessed part of is used. The dot-shaped small recess formed in order to change the traveling direction of light optimizes the shape, shape arrangement, size, distribution, etc. For example, the cross-sectional shape of the dot-shaped small recess is triangular, and the cross-sectional inclination angle is 50 to 60 degrees, and the dot-shaped small recess is almost rectangular or nearly square in plan view seen from the direction perpendicular to the light guide plate surface. At the same time, this substantially rectangular long side or almost square one side is provided substantially parallel to the longitudinal direction of the light source.

With such a configuration, in the case of the backlight, the light emitted in the lower surface direction of the light guide plate, that is, the reflective sheet direction is reduced, the output light emitted to the liquid crystal cell is increased, and the light component in the vertical direction of the output light is increased. By doing so, the luminance of the liquid crystal display device can be improved without raising the luminance of the light source, and the luminance distribution of the liquid crystal display device can be optimized, and the visibility can be improved. In the case of the front light, the light emitted directly from the light guide plate to the observer side is reduced, the light emitted to the liquid crystal cell is increased, and the light component in the vertical direction of the emitted light is increased, thereby increasing the brightness of the light source. The luminance of the liquid crystal display device can be improved, and the luminance distribution of the liquid crystal display device can be corrected, thereby improving visibility.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail based on drawing.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing of the backlight means used for the edge type backlight type liquid crystal display device which concerns on one Embodiment of this invention, The dot small recessed part formed in the back surface side of the light-guide plate is shown in a part of the same figure. And a partially enlarged perspective view as seen through. In addition, the backlight means of this embodiment is equipped with the light source 1, the light guide plate 2, and the reflective sheet 7 as a minimum component.

As shown in Fig. 1, the light guide plate 2 of the backlight means is formed to become thinner as the plate thickness moves away from the light source 1, and the light guide plate 2 has a light exit surface to the liquid crystal display element. A large number of dot-shaped small recesses 9 are formed on the surface on the opposite side (the surface on which the reflective sheet 7 is placed on the back surface in FIG. 1). The dot-shaped small concave portion 9 is formed in a substantially rectangular or almost square plane shape as viewed from the direction perpendicular to the light guide plate 2, and this substantially rectangular long side or nearly square one side of the light source 1 It is provided so as to be substantially parallel to the longitudinal direction (it is provided so as to be substantially orthogonal to the X axis in FIG. 1). In addition, the dot-shaped small recessed part 9 is formed so that the cross-sectional shape may be triangular, and the cross-sectional inclination-angle is 50-60 degrees in the cross section along the X-axis in FIG.

In the structure shown in FIG. 1, the light emitted from the elongate light source 1 provided in one end surface (incident cross section 8) of the light guide plate 2 is collected by the reflector 14, and serves as the incident light 10. As shown in FIG. It is introduced into the light guide plate 2 from the incident end surface 8 of the light guide plate 2, and becomes the waveguide 12, and the end face 11 on the side opposite to the incident end surface 8 of the light guide plate 2 (cross section on the right side in FIG. 1). Toward the surface of the light guide plate 2, the reflection is repeated on the back surface 13 and the light exit surface (light transmitting surface) 16 of the light guide plate 2.

The light incident on the inclined surface 15 of the dot-shaped small concave portion 9 among the waveguides 12 is reflected by the inclined surface 15, and a part of the light reaches the light exit surface (light transmitting surface) 16, It is refracted therefrom and exits from the light exit surface 16, passes through a diffusion sheet or prism sheet (not shown), and then enters the liquid crystal cell as illumination light. In addition, the light transmitted through the rear surface 13 of the waveguide 12 is reflected by the reflection sheet 7 and returned to the light guide plate 2 again, and the reflection progresses while repeating the reflection. A part of the light that hits the light exits from the light exit surface 16 in the same manner as above to become the illumination light of the liquid crystal display device.

Since the light intensity in the light source 1 generally decreases as it moves away from the light source 1 in the light guide plate 2, the density of the dot small recesses 9, that is, the dot small recesses per unit area is thereby reduced. The number of sections 9 is changed so that the intensity distribution of the illumination light, i.e., the backlight brightness, becomes uniform over the entire surface of the light guide plate 2. In the present invention, in the case of a single light source, the density of the dot-shaped small recesses 9 is increased exponentially or progressively from the incident end face 8 on the light source side toward the end face 11 on the opposite side. It is preferable to form.

Therefore, the reason why the light from the light source can be efficiently used for display by using the light guide plate of the embodiment of the present invention will be described. In general, the reflectance of the reflective sheet 7 is 95%. That is, about 5% of light is lost for each reflection. In the conventional light guide plate, about half of the light incident on the light guide plate is emitted from the back surface of the light guide plate while propagating the light guide plate, is incident on the reflective sheet, reflected there, and returns to the light guide plate again. That is, in the conventional light guide plate, the reflection is repeated a plurality of times between the light guide plate and the reflective sheet to lose about 5% of the light intensity. For this reason, in a conventional light guide plate, it is difficult to obtain a highly efficient backlight. In contrast, in the light guide plate of the present invention, since the amount of light emitted downward from the inclined surface 15 of the dot-shaped small concave portion 9 is small, the amount of light incident on the reflective sheet is small, and the loss by the reflective sheet is small. High brightness backlight is obtained.

Features of the light guide plate according to the present invention described above will be described in detail with reference to FIG. 5. FIG. 5 is a diagram showing a light guide plate 2 having a dot-shaped small recess 9 having a triangular cross section having a cross-sectional inclination angle of 55 °, and a propagation (advancing) trajectory of light incident on the light guide plate 2.

In the light guide plate 2, light having an extended angle of about ± 35 ° with respect to the horizontal line shown in FIG. 5 is advanced. Light incident on the dot-shaped small recess 9 in the triangular cross section is reflected and refracted by the inclined surface 15. Among these, the light reflected from the inclined surface 15 is emitted from the light exit surface 16 of the light guide plate 2 by changing the traveling direction upward in FIG. 5 to become illumination light of the liquid crystal display element. On the other hand, the light refracted by the inclined surface 15 is once emitted to the air layer, and then enters the inclined surface 15 on the opposite side, is refracted therein, and then returns to the light guide plate 2 again to enter the light guide plate 2. Proceed. The light traveling in the light guide plate 2 is reflected by the inclined surface 15 of the other dot-shaped recessed portion 9, and part of the light is emitted from the light exit surface 16 of the light guide plate 2 to display the liquid crystal display. It becomes the illumination light of the device. As described above, in the light guide plate 2 according to the present invention, since the amount of light incident on the reflective sheet 7 disposed on the rear surface side of the light guide plate 2 is small, the loss caused by the reflective sheet 7 becomes small, and as a result, High efficiency, high brightness backlight can be realized. In addition, in FIG. 5, A1-A7 show the trajectory of each light ray which reflects or refracts.

On the other hand, as shown in FIG. 6, when the cross-sectional inclination angle of the dot-shaped small recessed part of the light-guide plate 2 is small at 35 degrees, the light ray which refracted the inclined surface of the dot-shaped small recessed part turns into the light guide plate 2 It enters the reflective sheet 7 without going away and loses energy. In addition, in FIG. 5, B1-B6 has shown the trajectory of each light ray which reflects or refracts.

Similarly, in the case of the printed dot formed by printing the light diffusing material shown in FIG. 7A, the cross-sectional shape shown in FIG. 7B is the case of a ladder-shaped dot-shaped recess, or the cross-sectional shape shown in FIG. 7C Even in the case of the convex dot small convex portions, a considerable proportion of the light incident on the printing dot, the cross-sectional ladder type small concave portion, or the dot small convex portion does not return in the light guide plate 2, but the reflective sheet 7 Incident on it, the light energy is lost.

As described above, in the backlight type liquid crystal display device using the light guide plate according to the embodiment of the present invention, the light incident on the light guide plate than the conventional light guide plate is not borrowed with the aid of reflection, and the dot-shaped recess 9 ), The light emitting surface 16 can be efficiently emitted to the opposite side (light emitting surface 16). Therefore, the high efficiency and high brightness of a backlight are achieved by this.

The above-described principle of operation of the light guide plate in the backlight type liquid crystal display device can be applied to the front light type liquid crystal display device.

8 is a diagram showing the configuration of a front light type liquid crystal display device of an edge light system according to another embodiment according to an embodiment of the present invention. In the front-lit liquid crystal display device, the dot-shaped small concave portion 9 of the light guide plate 2 is located on the upper surface (surface opposite to the light exit surface 16 to the liquid crystal display device) in FIG. 8. It is formed in the same shape, shape arrangement and size distribution as the light guide plate in the backlight.

When the light guide plate 2 according to the embodiment of the present invention is used, in the front light type liquid crystal display device, the light emitted from the light guide plate 2 is only on the back surface (light exit surface 16) of the color filter. And efficiently exit toward the liquid crystal display element made of the reflective liquid crystal layer 15 and the reflective polarizer 52. That is, in FIG. 8, the amount of light emitted upward from the light guide plate 2 (light emitted directly upward rather than toward the liquid crystal display element) is small, and is incident from the light guide plate 2 toward the lower side, that is, the liquid crystal display element direction. The light quantity becomes large, the front-light reflection type liquid crystal display device with the good utilization efficiency of the light in the light source 1, and good visibility can be implement | achieved.

9A to 9D show an example of the shape of the dot-shaped small recess 9 formed in the light guide plate 2, and the plane shape thereof is almost rectangular as in FIGS. 9A and 9B, or as shown in FIGS. 9C and 9D. It is preferable to use the dot-shaped small recessed part 9 whose planar shape is substantially square.

The table of FIG. 10 summarizes the most preferable embodiment of the dot small recessed part 9 in the Example of this invention, Comprising: The cross-sectional shape, cross-sectional inclination-angle, inclination-angle distribution, depth of the dot-shaped small recessed part 9 Specific contents such as planar shape, density distribution, shape distribution, size, wiring, and the like are shown.

Prior to describing the dot-shaped small recess 9 of the embodiment of the present invention based on FIG. 10, the definition of various parameters, a determination method, and the like will be described.

First, the depth d of the dot-shaped small recess 9 is defined as shown in Fig. 11A. That is, the maximum value of the distance between the light guide plate 2 surface and the concave bottom surface of the dot small recessed part 9 is defined as the depth d of the dot small recessed part 9.

In addition, the cross-sectional inclination angle (alpha), (alpha) 'of the dot-shaped small recessed part 9 is a point a, b, or a' which the horizontal line which passes through the point which divided the depth d by 3 crosses an inclined surface, as shown in FIG. It defines as the line segment which connects b ', and the angle formed with the light-guide plate 2 surface.

In addition, when the planar shape of the dot-shaped small recessed part 9 (planar shape which saw the dot-shaped small recessed part 9 in the direction perpendicular | vertical to the light guide plate 2) is almost rectangular, the length L of a long side, and a short side The length Ws is defined as shown in Fig. 11B, respectively.

Next, based on the table of FIG. 10, the detail of the specific content of the most preferable example of the dot-shaped small recessed part 9 is described.

First, the dot-shaped small recess 9 of the embodiment of the present invention is natural, but it is essential that it is concave. One of the reasons for this is that the luminance improvement effect can be obtained as described above by making the concave shape. Another reason for the concave shape is a difference in formability in comparison with the convex shape when the light guide plate 2 is to be obtained by plastic molding. That is, it is because the fluidity | liquidity with respect to the formation site | part of the dot small recessed part in a metal mold | die becomes favorable compared with that in the formation site | part of the dot small convex part in a metal mold | die. This is because in the case of dot-shaped small convex portions, the mold surface is concave, and when resin flows, air masses are likely to occur at the tip of the concave portion of the mold, and the transferability of the plastic light guide plate material to the mold surface deteriorates. This is because in many cases, only incomplete dot type small convex portions can be provided. On the other hand, in the case of a dot small recessed part, the transfer property to a metal mold | die surface is favorable, and the dot small recessed part of a desired shape can be obtained easily.

The formation surface of the dot small recesses 9 is the surface opposite to the light exit surface 16 in the light guide plate 2, and in the case of the backlight, the formation surface of the dot small recesses 9 is shown in FIG. In the case of a front light, the forming surface of the dot-shaped small recessed part 9 is an upper surface in FIG.

The reason for setting the cross-sectional shape of the dot-shaped small recess 9 to be a triangle and setting the cross-sectional inclined film to 50 to 60 ° is as described above with reference to FIG. 5, and the light exit surface 16 of the light guide plate 2 is described. ) And the amount of light emitted from the light exit surface 16 of the light guide plate 2 is increased, and the amount of light emitted from the surface (the side on which the dot-shaped small recess 9 is formed) becomes smaller. This is because the amount of emitted light in the vertical direction with respect to the exit surface 16 tends to increase.

It is preferable that the planar shape of the dot-shaped small recessed part 9 be made into half or more nearly square or nearly square. The planar shape of the dot-shaped small recessed part 9 is made into substantially rectangular or nearly square, and the long side or nearly square one side of a rectangle is parallel to the longitudinal direction of the cold cathode tube or hot cathode tube which is the light source 1, It is desirable to arrange so as to lose weight.

The reason why the planar shape of the dot-shaped small concave portion 9 is made almost rectangular and almost square, and the long side or one side thereof is parallel to the longitudinal direction of the light source 1 is to reduce scattered light in the light guide plate 2. This is to improve the brightness by making it. The light emitted from the light source 1 is introduced into the light guide plate 2 at the incident end surface 6 of the light guide plate 2, proceeds inside the light guide plate 2, and part of the dot-shaped recesses 9 are formed. The light incident on the light guide plate 2 changes the traveling direction of the light, and part of the light incident on the dot-shaped small recess 9 is emitted from the light exit surface 16 of the light guide plate 2 toward the liquid crystal display element. Here, it is preferable that the light incident on the dot-shaped small recess 9 is emitted in a direction perpendicular to or perpendicular to the light exit surface 16. In contrast, most of the light rays incident on the light guide plate 2 from the light source 1 travel in a horizontal direction substantially perpendicular to the longitudinal direction of the light source 1. Then, a part of the light incident on the inclined surface 15 of the dot-shaped small concave portion 9 is reflected there and is emitted from the light exit surface 16. Therefore, in order to efficiently emit the incident light from the light exit surface 16, it is preferable that the inclined surface 15 of the dot-shaped small recess 9 faces the area as large as possible with respect to the traveling direction of the light. The dot-shaped small recess 9 having a substantially rectangular or nearly square planar shape is disposed at its long side or one side in parallel with the longitudinal direction of the light source 1. By doing in this way, the light guide plate 2 with a good reflection efficiency (light utilization efficiency) can be obtained, without increasing the number of the dot-shaped small recesses 9 blindly.

In addition, the planar shape of the dot-shaped small recessed part 9 is not limited to the above-mentioned substantially rectangular or almost square shape, but in order to improve the uniformity of a brightness distribution, a planar shape may vary depending on the site | part of the light guide plate 2. It may be possible to obtain favorable characteristics by using the circular or triangular dot-shaped small recess 9.

Next, the size of the dot small recessed part 9 in the case where the planar shape of the dot small recessed part 9 is substantially rectangular is demonstrated.

The length of the short side of the dot-shaped small recessed part 9 is 10-100 micrometers, and the length of the long side becomes like this. Preferably it is 1.5 times or more of a short side, and should be 500 micrometers or less. The reason for limiting the length of the cross section and the long side as described above is that when forming the circular shape of the dot-shaped small recessed portion on the glass disk by photolithography technique, it is desired to be thinner than 10 μm, and the dot-shaped small recessed portion having the desired contour This is because a problem of difficulty in obtaining a shape occurs. That is, when the size of the dot-shaped small recess is thinned, the resolution of the photomask, the exposure and the resolution of development occur, and the outline of the line of the dot-shaped small recess is jagged or the surface precision of the cross section is deteriorated. As a result, the light guide plate with little light scattering and high luminance cannot be obtained. As a means to solve this problem, there is a method of using a high resolution photomask and a high-precision exposure apparatus in photolithography. When using an exposure apparatus such as a high resolution mask such as a metal mask or a reduced exposure method, the production cost of the glass master This becomes expensive and as a result, it becomes impossible to provide a cheap light guide plate. When the length of the short side is 10 µm or more, the use of a laser drawing film photomask or an industrially inexpensive close-type exposure apparatus can be used, and the glass master and the metal stamper using the same can be produced at low cost.

On the contrary, limiting the length of the short side to 100 μm or less means that if the length of the short side is longer than this, the width area seen from the plane of the dot-shaped small recess 9 becomes large, so that the vanity of the dot-shaped small recess is visible. This is because it has been experimentally confirmed that the light guide plate 2 appears as an aggregate of point light sources) or that adjacent dot-shaped recesses 9 overlap.

In addition, making the length of the long side 1.5 times or more of the length of the short side more specifically, in order to prevent the number of the dot-shaped small recesses 9 from becoming obscurably, This is to increase the area of the inclined surface 15 of the dot-shaped small recess 9 which is effective in changing the traveling direction of light without increasing the number of the dot-shaped small recesses 9.

In addition, limiting the length of the long side to 500 μm or less means that the dot-shaped small recess 9 becomes too large and the vanity of the dot-shaped small recess 9 occurs, or the quality of the back light or the front light is longer than this. In other words, it has been confirmed experimentally that the quality deteriorates. In other words, when the size of the dot-shaped recesses 9 is large, when the liquid crystal display device is brought close to each other, the dot-shaped recesses 9 serving as the bright spots of the backlight or the front light can be visually discriminated. This is because it interferes with discriminating characters and pictures indicated by the liquid crystal display.

Next, the arrangement according to the size of the dot-shaped small recess 9 will be described.

The size of the dot small recesses 9 in the center portion in the direction parallel to the longitudinal direction of the light source 1 of the light guide plate 2 (in the Y direction in FIG. 1) is the dot small recesses at both ends in the Y direction. The smaller it is compared with the size of the part 9, the better. This reason is for uniformizing the luminance distribution in the direction parallel to the longitudinal direction of the light source 1 (Y direction in FIG. 1).

In general, when the size of the dot-shaped small concave portion 9 is made constant, the luminance of both ends of the light guide plate 2 in the Y direction (see FIG. 1) is lower than that of the center portion. This is because the supply amount of light from the light source 1 is relatively small at both ends of the light guide plate 2 in the Y direction compared to the center portion in the Y direction. In the prior art, in order to solve this problem, the luminance of the center portion was deliberately lowered to improve the luminance of both ends in the Y direction relatively, and to uniformize the luminance distribution of the entire light guide plate 2 (the entire liquid crystal display element). This has been a path for improving the brightness of the back light and the front light.

On the other hand, in the embodiment of the present invention, the size of the dot small recesses 9 in the center portion in the Y direction is made smaller than the size of the dot small recesses 9 in the both ends in the Y direction, In the center part, the total value of the area of the inclined surfaces of both ends of the Y-direction in the dot-shaped small recesses 9 (the area of both edges of the Y-direction of the dot-shaped small recesses 9) is increased, whereby it is considered as a vector. The component of the light traveling in the parallel direction with respect to the longitudinal direction of the light source 1 is increased. That is, the light quantity of the center part of the Y direction of the light guide plate 2 is sent to the both ends of the Y direction of the light guide plate 2, and uniformly distributes the light beam distribution of the whole light guide plate 2 (the whole liquid crystal display element). In this manner, the luminance distribution can be uniformized without lowering the luminance.

In addition, the luminance distribution of the entire light guide plate 2 (the entire liquid crystal display element) is equalized by reducing the size of the dot-shaped small recess 9 from the downstream side as the upstream side of the light traveling plate 2 in the traveling direction. Contribute to This is because the luminance of the downstream side in the traveling direction of the light of the light guide plate 2 is lower than that of the upstream side when the size of the dot-shaped small recess 9 is made constant.

Next, the distribution of the density (number of dot small recesses per unit area) of the dot small recesses 9 will be described.

In order to achieve uniform luminance distribution, the density of the dot-shaped small recesses 9 decreases as the closer to the light source 1, that is, the upstream side of the light traveling direction.

In addition, the density of the dot-shaped small recessed part 9 is the density | concentration of the dot-shaped small recessed part 9 in the center part of the Y direction of the light guide plate 2, in order to aim at uniformization of brightness distribution. It is made smaller than that of both ends. In addition, a part or all of the planar shape of the dot-shaped small recessed part 9 formed in the both ends of the light-guide plate 2 in the Y direction is made into the shape of small areas, such as square other than a rectangle, a circle, a triangle, etc. as needed. do.

In addition, it is effective that the individual arrangement of the dot-shaped small recesses 9 is randomized over the entire surface of the light guide plate 2. The reason for this is that the dot small recesses 9 of the present invention are fine, so that when the individual arrangement of the dot small recesses 9 is irregular, other members constituting the liquid crystal display device, for example, a liquid crystal cell, This is because moiré caused by interference with regular patterns such as color filters, TFT patterns, and black stripes can be prevented.

Next, the appropriate value of the depth d of the dot-shaped small recessed part 9 is described. The depth d of the preferable dot-shaped recessed part 9 is 1-200 micrometers, especially 1-100 micrometers.

When the depth d of the dot-shaped small recessed portion 9 is 1 µm or more, if it is shallower, the area of the inclined surface 15 of the dot-shaped small recessed portion 9 becomes smaller, and the light rays incident on the light guide plate 2 are made. This is because the function of changing the advancing direction becomes smaller, and it becomes difficult to improve the light emission efficiency of the light on the light exit surface 16 of the light guide plate 2 to a predetermined value or less.

On the other hand, when the depth d of the dot-shaped small concave portion 9 is 200 µm or less, if the depth d is deeper than this, the amount of emitted light on the upstream side in the advancing direction in the light guide plate 2 becomes too large, so as to achieve uniformity in luminance distribution. The reason for this is that it is difficult to make correction, and the tendency of decreasing the uniformity of the luminance of the light guide plate 2 as a whole tends to appear.

Next, the cross-sectional inclination angle of the dot-shaped small recessed part 9 is demonstrated.

The cross-sectional inclination angle of the dot-shaped small recessed part 9 is defined as (alpha), (alpha) 'of FIG. 11A as mentioned above. Preferable alpha, alpha 'is 50-60 degrees, 53-57 degrees are especially preferable. This is because the reflection function for changing the traveling direction of the light is large, the transmitted light is easily suppressed, and as a result, high luminance can be obtained.

Next, the manufacturing method of the light guide plate used for the backlight type liquid crystal display device or the front light type liquid crystal display device of the Example of this invention is demonstrated.

The light guide plate of the Example of this invention is basically manufactured by manufacturing a metal mold | die and plastic molding. As a manufacturing method of this metal mold | die, various machining methods, for example, a method of a drill, cutting, grinding, etc. can be used, and an electric discharge process is also an effective means. However, since the dot-shaped small recess of the light guide plate of the present invention has a general design, the number thereof is 200 to 20000 / cm ^2, and there are more than 1 million in the entire light guide plate, so that a large number is applied. It is good.

12A to 12K are process drawings showing one embodiment of a method of manufacturing the light guide plate 2 according to the embodiment of the present invention.

The manufacturing method shown to FIG. 12A-12K,

(1) a step of subjecting the Si substrate 20 having the oxide film (SiO ₂ film) 21 formed thereon to improve the adhesion of the photoresist;

(2) forming the photoresist 22 on the Si substrate 20 (FIG. 12A),

(3) A step of disposing a photomask 23 having a pattern of dot-shaped small recesses on the Si substrate 20 and irradiating ultraviolet (UV) light from the upper side of the mask 23 (photoresist 22). Selective exposure curing) (FIG. 12B),

(4) Thereafter, the photoresist 22 is developed (by removing the uncured photoresist 22) to form a pattern of dot-shaped small recesses by the photoresist 22 on the Si substrate 20. Process (FIG. 12B, C),

(5) Process of attaching the protective tape 24 to the predetermined surface of the Si substrate 20, etching the oxide film (SiO ₂ film) 21 to form a pattern of dot-shaped small recesses by the oxide film 21 ( 12c),

(6) removing the remaining photoresist 22 (FIG. 12D),

(7) Process of carrying out semiconductive etching of the surface of Si substrate 20 using oxide film 21 as a mask (FIG. 12E),

(8) removing the oxide film 21 after removing the protective tape 24 (FIG. 12F),

(9) Process of Forming Plating Base Film 25 on Si Substrate 20 (FIG. 12G),

(10) Process of plating (Ni plating) using plating base film 25 as an electrode, then peeling it to obtain master stamper 26 (FIG. 12H),

(11) An extremely thin peeling layer (an ultra thin film peeling layer of an electroplatable degree) is formed on a predetermined surface of the master stamper 26, and the master stamper 26 is plated, and then the film is peeled off to form a mother stamper 27. ) (FIG. 12i),

(12) An extremely thin peeling layer (an ultra thin film peeling layer of an electroplatable degree) is formed on a predetermined surface of the mother stamper 27, and the mother stamper 27 is plated, and then peeled off to form a stamper for forming. 28) to obtain (Fig. 12j),

(13) a step of finishing polishing the forming surface of the dot-shaped small recess of the molding stamper 28 as necessary;

(14) a step of polishing the back surface of the molding stamper 28 (the surface opposite to the surface on which the dot-shaped small recess is formed);

(15) a step of attaching a molding stamper 28 to an injection molding machine to obtain a light guide plate 2 by injection molding (FIG. 12K);

Is done.

In the above-mentioned manufacturing process, before forming the photoresist 22, it is extremely important to perform a process of applying a primer which is an adhesion improving agent between the Si substrate 20 and the photoresist. As the primer treatment method, it is appropriate to use a silane-based chemical as a primer, and hexamethylsilazane is mentioned as a specific example. The gas diffusion method is preferred as the method for treating hexamethylsilazane. The gas diffusion method is a method of forming a thin film on the surface of a substrate by evaporating hexamethylsilazane in a container and is most suitable for forming a uniform film.

As the photoresist material, a liquid or film type positive or negative tab material can be used. In the example shown in FIGS. 12A to 12K, a process in the case of using a positive material is illustrated. The formation method includes a spin coating method and a roll coating method.

The photomask 23 can use a chrome mask, a film mask, an emulsion mask, and can prepare by drawing data, such as the shape, size, and number distribution of the dot-shaped small recessed part previously designed, and drawing by an electron beam, a laser beam, etc. have.

Here, anisotropic etching of Si is demonstrated. It is extremely effective to use the anisotropic etching method of single crystal Si after the cross-sectional shape by this invention forms a triangular dot-shaped recessed part. This etching method uses the etching rate by the crystal orientation of Si crystals. A crystal having a (100) plane is used as the Si crystal substrate, and a KOH aqueous solution is used as the etching solution. The concentration is about 20%. The etching rate of the (100) plane is shown in FIG. By etching under the above conditions, a dot-shaped small concave portion having an isosceles triangular cross section having a cross-sectional inclination angle of about 55 ° can be formed.

14 shows the specific examples of the processing conditions of the Si substrate 20 described above in a table.

If the plating base film 25 is formed before the plating layer (master stamper) 26 is formed, the traces of the plating process disappear and a good plating layer, that is, the master stamper 26 can be formed. As the plating base layer 25, a sputtered film such as a Ni thin film can be used, but this film thickness is an extremely important parameter. If the plating base film 25 is thickened, a problem occurs that the film peels off during plating. In the manufacturing method of this invention, it is important to control the film thickness of the plating base film 25 to 150-350 GPa, especially 200-300 GPa. When the film thickness of the plating base film 25 is thinner than this, a uniform plating plate cannot be manufactured when plating is performed. On the other hand, when the plating base film 25 is formed thicker than this, there arises a problem that the plating base film or the dot-shaped small recess pattern peels during plating, and thus a good master stamper 26 cannot be obtained.

Although various metals can be used as the material of the plating base film 25 and the plating layer (master stamper) 26, Ni is an optimal material in terms of uniformity and mechanical performance. The obtained plating layer (master stamper) 26 can be easily peeled off from the Si substrate 20.

Polishing the formed surfaces of the dot-shaped small recesses of the obtained master stamper 26, mother stamper 27, and molding stamper 28 is important for obtaining the light guide plate 2 having high luminance. In particular, polishing of the master stamper 26 is important, and this polishing determines the surface roughness of the mother stamper 27 and the forming stamper 28. Polishing can be performed by hand roughing and mechanical roughening with alumina abrasive grains or diamond abrasive grains having an average particle diameter of 0.1 to 1 µm. Thereby, the surface roughness of the light guide plate 2 of the obtained molded article is improved, and a light guide plate with high brightness can be obtained.

The obtained molding stamper 28 is accurately positioned and fixed to a predetermined portion of the mold of the injection molding machine, for example, by a magnet, a vacuum chuck, etc., and the light guide plate 2 is continuously produced with good productivity by known injection molding. Moreover, as a shaping | molding method other than this, it is also possible to shape | mold the light guide plate 2 by extrusion molding, compression molding, vacuum molding, etc.

As a material constituting the light guide plate 2, a transparent plastic material can be used. Specific examples include acrylic plastics, polycarbonate resins, polyacetal resins, polyolefin resins, and ultraviolet curable plastic materials. Among these, the acrylic material is excellent in transparency, price, and moldability, and is a material suitable for the light guide plate 2 according to the present invention.

15 is a schematic diagram of the configuration of a backlight liquid crystal display device according to an embodiment of the present invention. On the upper surface of the light guide plate 2 used as a component of the backlight means, a diffusion sheet 3, a prism sheet 5, 5 ', a polarizing plate 17, a liquid crystal cell 51, a color filter 52, a polarizing plate 17 is arranged. This structure shows the general example of a liquid crystal display device, and various deformations are considered including a back lighting part according to the use of a display device.

For example, a wide viewing angle is particularly required for a desktop display device or a television monitor of a personal computer. In this case, a diffuser plate that scatters illumination light and expands the viewing angle is newly placed at an appropriate position (for example, of a liquid crystal panel). On the top). Further, in order to widen the viewing angle, a sheet having a light diffusing effect may be disposed, or the light transmitting surface may be processed to give a light scattering function to increase the viewing angle.

Specific examples of the light source 1 used in the embodiment of the present invention include a cold cathode tube, a hot cathode tube, a tungsten lamp, a xenon lamp, a metal halide lamp, and the like, and a light source of a low temperature system such as a cold cathode tube is usually used. This is preferred.

In addition, there is no limitation in particular about the liquid crystal display element or liquid crystal cell used by the Example of this invention, A well-known element and a panel can be used. As a general liquid crystal cell, the thing of the twisted nematic type | mold, the super twisted nematic type | mold, the homodiase type | mold, a thin film transistor type, an active matrix drive type | mold, a simple matrix drive type | mold, etc. are mentioned.

Although the embodiments of the present invention have been mainly described above, various modifications are possible to those skilled in the art without departing from the spirit of the present invention.

According to the embodiment of the present invention as described above, it is possible to provide a light guide plate and a liquid crystal display device using the same that can improve the brightness of the back light or the front light without increasing the brightness of the light source. Further, according to the embodiment of the present invention, it is possible to realize a light guide plate having stable characteristics without generation of moiré, which has been a problem in the structure of the conventional apparatus, high light utilization efficiency, and no occurrence of luminance unevenness, and a liquid crystal display device using the same. Moreover, according to the Example of this invention, the high-performance light guide plate for liquid crystal display devices can be manufactured at low cost with good mass productivity.

Claims (19)

A liquid crystal cell, a light guide plate for a backlight or a front light guide provided on the back or front of the liquid crystal cell, and a light source provided on one end surface of the light guide plate and irradiating light into the light guide plate from one end surface of the light guide plate. In the liquid crystal display device, On the surface opposite to the light exit surface from the light guide plate to the liquid crystal cell, a plurality of dot small recesses for reflecting the incident light from the light source in the light exit surface direction are formed, the cross-sectional shape of the dot small recesses The angle of inclination of the cross section is set to 50 to 60 degrees, and the dot-shaped small concave portion makes the planar shape viewed from the direction perpendicular to the light guide plate surface almost rectangular or nearly square, A long side or a substantially square side is provided in substantially parallel to the longitudinal direction of the light source. The said substantially rectangular or substantially square shape in the said dot small recessed part is a length of the short side 10-100 micrometers, The long side is 1.5 times or more of the length of a short side, and 500 micrometers or less. The depth of the dot-shaped small concave portion is 2 to 100 µm. The liquid crystal display device according to claim 1, wherein a dot-shaped small recess other than the shape described above is formed on a surface on the side opposite to the light exit surface in the light guide plate. The liquid crystal display device according to claim 1, wherein the individual arrangements of the dot-shaped small concave portions are made almost random over the entire light guide plate. The liquid crystal display device according to claim 1, wherein the number per unit area of the dot-shaped small concave portion in the light guide plate is increased as the distance from the light source side increases. The liquid crystal display device according to claim 1, wherein the size of the dot-shaped small concave portion in the light guide plate is made larger as it moves away from the light source side. 2. The liquid crystal display device according to claim 1, wherein the number per unit area of the dot-shaped small recessed portion along the direction parallel to the longitudinal direction of the light source in the light guide plate is increased at the end portion than the center portion. The liquid crystal display device according to claim 1, wherein the size of the dot-shaped recesses along the direction parallel to the longitudinal direction of the light source in the light guide plate is made larger at the end than at the center. The liquid crystal display device of claim 1, wherein the light guide plate is thinner as the thickness of the light guide plate moves away from the light source. In the light guide plate which introduces light from the light source provided in the one end surface, On the surface opposite to the light exit surface of the light guide plate, a plurality of dot small recesses for reflecting the incident light from the light source in the light exit surface direction are formed, and the cross-sectional shape of the dot small recesses is triangular. At the same time, the cross-sectional inclination angle is set to 50 to 60 °, and the dot-shaped small concave portion makes the planar shape viewed from the direction perpendicular to the light guide plate surface almost rectangular or almost square, and at the same time the substantially rectangular long side or nearly square A light guide plate, wherein one side is provided in substantially parallel to the longitudinal direction of the light source. The said substantially rectangular or substantially square shape in the said dot-shaped small recessed part is a length of the short side 10-100 micrometers, The long side is 1.5 times or more of the length of a short side, and 500 micrometers or less And the depth of the dot-shaped small concave portion is 2 to 100 µm. The light guide plate according to claim 10, wherein a dot-shaped small recess other than the above-described shape is formed on a surface on the side opposite to the light exit surface of the light guide plate. The light guide plate according to claim 10, wherein the individual arrangements of the dot-shaped small recesses are almost random over the entire light guide plate. The light guide plate according to claim 10, wherein the number per unit area of the dot-shaped small concave portion in the light guide plate is increased as the distance from the light source side increases. The light guide plate according to claim 10, wherein the size of the dot-shaped small concave portion in the light guide plate is increased as the distance from the light source side increases. The light guide plate according to claim 10, wherein the number per unit area of the dot-shaped recessed portion along the direction parallel to the longitudinal direction of the light source in the light guide plate is increased at an end portion rather than a center thereof. The light guide plate according to claim 10, wherein the size of the dot-shaped small concave portion along the direction parallel to the longitudinal direction of the light source in the light guide plate is made larger at the end than at the center. The light guide plate according to claim 10, wherein the light guide plate is formed thinner as the thickness of the light guide plate moves away from the light source. In the manufacturing method of the light guide plate of Claim 10, (a) depositing a photoresist on a Si crystal substrate having a SiO ₂ film formed thereon, and then forming a pattern of the dot-shaped small recesses in the photoresist using photolithography technology; (b) etching the SiO ₂ film using the photoresist as a mask, and then removing the photoresist; (c) anisotropically etching the Si crystal substrate using the SiO ₂ film as a mask, forming the dot-shaped small recesses in the Si crystal substrate, and then removing the SiO ₂ film; (d) forming a metal film serving as a plating base film on the Si crystal substrate, performing Ni plating using the metal film as an electrode, forming a master stamper using a Ni plated plate, and peeling it from the Si crystal substrate; , (e) plating the master stamper to form a mother stamper, and peeling it from the master stamper; (f) plating the mother stamper to form a molding stamper, and peeling it from the mother stamper; (g) attaching the molding stamper to a molding machine to manufacture the light guide plate by molding; Method of manufacturing a light guide plate comprising a.